1. Field of the Invention
The present invention relates to an electron source for emitting an electron beam and a process for producing the electron source. The present invention also relates to an image-forming apparatus such as an image-displaying apparatus for forming an image on irradiation of an electron beam.
2. Related Background Art
Two kinds of electron-emitting elements are known: thermoelectron sources and cold cathode electron sources. The cold cathode electron sources include field emission type electron sources (hereinafter referred to as "FE"), metal/insulator/metal type electron sources (hereinafter referred to as "MIM"), surface conduction electron-emitting elements, and the like.
The above FE is exemplified by the ones disclosed by W. P. Dyke & W. W. Dolan ("Field emission": Advance in Electron Physics, 8, 89, (1956)), C. A. Spindt ("Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones": J. Appl. Phys, 47, 5248, (1976)), etc.
The above MIM is exemplified by the ones disclosed by C. A. Mead ("The Tunnel-Emission Amplifier": J. Appl. Phys., 32, 646 (1961), etc.
The above surface conduction electron emitting element is exemplified by the ones disclosed by M. I. Elinson (Radio Eng. Electron Phys. 10, (1965)), etc.
The surface conduction electron-emitting element utilizes the phenomenon that electrons are emitted by flowing an electric current through a thin film formed with a small area on a substrate and in parallel to the surface of the film. Such surface conduction electron-emitting elements include, in addition to the above-mentioned one disclosed by Elinson employing an SnO.sub.2 thin film, the ones employing an Au thin film [G. Ditter: "Thin Solid Films", 9, 317, (1972)], the ones employing In.sub.2 O.sub.3 /SnO.sub.2 thin film [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)], the ones employing a carbon thin film [H. Araki et al.: Sinkuu (Vacuum), Vol. 26, No. 1, p. 22 (1983), and so forth.
Typically, the surface conduction electron-emitting element has an element constitution as shown in FIG. 23 disclosed by M. Hartwell as mentioned above. In FIG. 23, the numeral 231 denotes a substrate, and the numeral 232 denotes a thin film for electron-emitting region formation (hereinafter referred to as "emitting region-generating thin film") composed of a thin metal oxide film or the like formed in an H-shaped pattern by a sputtering process. On the thin film 232, an electron-emitting region 233 is formed by voltage application called a "forming" treatment as described later. The numeral 234 denotes a thin film having an electron-emitting region.
In such surface conduction electron-emitting elements generally, the electron-emitting region 233 is formed by a voltage application treatment, i.e., forming, of an emitting region-generating thin film 232 prior to use for electron emission. The forming is a treatment of flowing electric current by application of voltage between the both ends of the emitting region-generating thin film 232, thereby the emitting region-generating thin film is locally destroyed, deformed, or denatured to have high electric resistance to form the electron-emitting region 233. The surface conduction electron-emitting element having been subjected to the forming treatment emits electrons from the electron-emitting region on application of voltage to the thin film 234 having the electron-emitting region 233.
Such conventional surface conduction electron-emitting elements have various problems in practical use. The inventors of the present invention, after comprehensive investigations, have solved the practical problems as described below.
For example, the inventors of the present invention disclosed a novel surface conduction electron-emitting element in which, as shown in FIG. 24, a fine particle film 244 is provided as the emitting region-generating thin film between electrodes (242, 243) on a substrate 241, and a fine particle film 244 is subjected to voltage application treatment to form an electron-emitting region 245 (Japanese Patent Application Laid-Open No. 2-56822).
In another example of electron sources, in which a number of surface conduction electron-emitting elements are arranged in lines, and the both ends of the respective elements in each line are connected in parallel by wiring (e.g., Japanese Patent Application Laid-Open No. 1-283749 applied by the present inventors).
In recent years, flat-panel display apparatuses employing liquid crystal have become popular in place of CRT as image-forming apparatus. However, the liquid crystal, which does not emit light spontaneously, requires back-light or the like disadvantageously. Therefore, an emissive display device is demanded.
To meet such demands, an image-forming device is disclosed in which an electron source having a number of surface conduction electron-emitting elements arranged therein is combined with a fluorescent material which emits light on receiving electrons from the electron source (e.g., U.S. Pat. No. 5,066,883 applied by the present inventors). Such an image-forming device enables relatively easy production of apparatuses of large picture area, and gives emissive display devices with high image quality.
Display devices and other image-forming apparatuses are necessarily expected to be larger in the picture size, and finer in image quality. In the above-mentioned electron sources having a number of electron-emitting elements arranged therein frequently encounter the problems as below:
1) Defectiveness or failure of the electron-emitting element itself, PA1 2) Disconnection in common wiring, or short circuit between adjacent wiring, and PA1 3) Insufficient insulation between layers at a cross-over portion.